International applications WO 93/25799 (which issued as U.S. Pat. No. 5,348,095), WO 98/00626 (which was filed as U.S. patent application Ser. No. 08/891,318) and WO 99/35368 (which was filed as U.S. patent application Ser. No. 09/223,996), the contents of which are incorporated by reference, concern the so-called ‘expandable-tube technology’ for well construction and wellbore repair. In short, this technology involves lowering a pipe (also referred to as ‘oilfield tubular’) of a malleable steel grade material into a borehole or existing casing, followed by an expansion process (e.g. by moving an expansion mandrel or pig through the pipe). The pipe may serve as a casing, or as a production tubing (liner) through which a hydrocarbon product is transported to the surface. Alternatively, the pipe may be expanded against the inner surface of a casing that is present in the borehole (e.g. as a protective cladding for protecting the well casing against corrosive well fluids and damage from tools that are lowered into the well during maintenance and work-over operations).
According to WO 93/25799 (which issued as U.S. Pat. No. 5,348,095), adjacent pipes may be joined using expandable threaded connections. For instance, a first casing may be provided with internal annular ribs having an inner diameter slightly larger than the outer diameter of a section of a second casing which extends into said section of the first casing. During expansion of the casing joint, the second casing is pressed against the ribs of the first casing, whereby a metal to metal seal is achieved between said section of the first and second casing.
International application WO 98/00626 (which was filed as U.S. patent application Ser. No. 08/891,318) describes a process for casing off the borehole of a gas or oil well which penetrates an underground formation. The method basically entails lowering a reeled pipe of a malleable steel grade into a borehole (which is created by conventional drilling methods), followed by an expansion process. International application WO 99/35368 (which was filed as U.S. patent application Ser. No. 09/223,996) is concerned with expandable tube technology for the production of slender wells and mono-diameter wells. According to this application casings are “bonded” and “sealed” by co-axial overlap between an expanded casing and an expandable casing followed by expansion of the latter. According to this application, it is preferred that the production tubing and at least one of the casings consists of a tubing which is inserted into the borehole by reeling the tubing from a reeling drum. Alternatively, the production tubing and/or at least one of the casings may be made up of a series of short pipes or pipe sections that are interconnected at the wellhead by screw joints, welding or bonding to form an elongate pipe of a substantially cylindrical shape that can be expanded and installed downhole in accordance with the method of that invention.
Expandable-tube technology therefore principally relies on lengthy pipes which are unreeled from a reeling drum into the borehole, or on short pipes that are equipped with treaded connections and that are interconnected on-site. However, either method has its drawbacks.
Good joint quality in (oil field) pipes is often essential or even critical as in gas wells. The welding technique typically employed is that of submerged arc welding (SAW), e.g., Tungsten Inert Gas welding (TIG welding). Pipes in the form of welded tubulars, wherein tubular elements are connected by TIG welding are for instance available from Well Engineering Partners B. V. (Holland) under the trademark “BIG LOOP”. Unfortunately, safety requirements do not generally allow TIG welding at or near the borehole. Another form of welding, electrical resistance welding (ERW) is unacceptable for the same reason. Welding at the rig floor therefore seems to be too risky.
Other methods exist for interconnecting tubular elements, such as radial friction welding, and amorphous bonding, as in WO 98/33619, which cannot be used on the rig either (for safety reasons, but also for reproducibility and quality control reasons).
The advantage of threaded connections is that the pipe may be assembled tailor-made on the rig itself. On the other hand, threaded connections are not gas tight, especially when expanded, which may cause undesirable migration of reservoir fluids, even leading to gas migration and blow out. Besides, these connections of which a typical casing or production liner will contain many hundreds, form the weakest part of the pipe (having a tensile strength that is only 50–60% of that of the pipe itself).
A further drawback of these methods is that the pipes so produced may burst or rupture, at the connections or elsewhere in the pipe, when expanded. The reason for this is that the expansion behaviour at the connections differs from that elsewhere in the pipe. For instance, if an expansion mandrel is used to expand the pipe, then it may get stuck. Alternatively, the force required to expand the connection may be more than the pipe is capable of handling. It would therefore be beneficial to achieve a method for interconnecting pipes in a manner that does not effect the expandability of the pipe. Ideally, this method should be sufficiently safe and simple to allow the pipes to be assembled from tubular elements on a rig floor.